US 8057575 B2
Hydrogen-producing fuel processing systems, hydrogen purification membranes, hydrogen purification devices, fuel processing and fuel cell systems that include hydrogen purification devices, and methods for operating the same. In some embodiments, operation of the fuel processing system is initiated by heating at least the reforming region of the fuel processing system to at least a selected hydrogen-producing operating temperature. In some embodiments, an electric heater is utilized to perform this initial heating. In some embodiments, use of the electric heater is discontinued after startup, and a burner or other combustion-based heating assembly combusts a fuel to heat at least the hydrogen producing region, such as due to the reforming region utilizing an endothermic catalytic reaction to produce hydrogen gas.
1. A hydrogen-producing fuel processing system, comprising:
a steam reforming chamber containing a steam reforming catalyst, wherein the steam reforming chamber is configured to receive a feed stream including methanol and water and produce a reformate stream therefrom, wherein the reformate stream contains hydrogen gas as a majority component and further includes other gases;
a membrane module configured to receive the reformate stream and divide the reformate stream into a byproduct stream and a hydrogen-rich stream, the membrane module comprising:
a plurality of hydrogen-selective membranes, each being generally planar and having a reformate side and a permeate side, wherein the plurality of hydrogen-selective membranes are spaced-apart from each other and oriented with their permeate sides generally facing each other to define a harvesting conduit extending therebetween, wherein the hydrogen-rich stream is formed from a portion of the reformate stream that passes through the plurality of hydrogen-selective membranes to the harvesting conduit, with a remaining portion of the reformate stream which remains on the reformate side of the plurality of hydrogen-selective membranes forming the byproduct stream, and further wherein the hydrogen-rich stream has a greater concentration of hydrogen gas than the byproduct stream;
a support within the harvesting conduit and configured to support the plurality of hydrogen-selective membranes, wherein the support includes a pair of generally opposed surfaces which are configured to provide support to a respective one of the permeate sides of the plurality of hydrogen-selective membranes; and
a product outlet port in fluid communication with the harvesting conduit and through which the hydrogen-rich stream is withdrawn from the membrane module; and
a polishing region configured to reduce a concentration of any carbon monoxide present in the hydrogen-rich stream and to produce a product hydrogen stream therefrom.
2. The hydrogen-producing fuel processing system of
3. The hydrogen-producing fuel processing system of
4. The hydrogen-producing fuel processing system of
5. The hydrogen-producing fuel processing system of
6. The hydrogen-producing fuel processing system of
7. The hydrogen-producing fuel processing system of
8. The hydrogen-producing fuel processing system of
9. The hydrogen-producing fuel processing system of
10. The hydrogen-producing fuel processing system of
11. The hydrogen-producing fuel processing system of
12. The hydrogen-producing fuel processing system of
13. The hydrogen-producing fuel processing system of
14. A method for starting operation of the hydrogen-producing fuel processing system of
electrically heating, during a startup period, the steam reforming catalyst to a selected hydrogen-producing operating temperature of at least 200° C.; wherein, when heated to the selected hydrogen-producing operating temperature, the steam reforming catalyst is configured to catalyze, via a steam reforming reaction, formation of the reformate stream from the feed stream;
ceasing the electrically heating;
delivering the feed stream to the steam reforming chamber;
producing the reformate stream from the feed stream;
separating the reformate stream into the hydrogen-rich stream;
reducing the concentration of carbon monoxide in the hydrogen-rich stream with the polishing region to produce the product hydrogen stream;
combusting at least a portion of the byproduct stream to produce a heated exhaust stream; and
heating at least the steam reforming catalyst with the heated exhaust stream to maintain the steam reforming catalyst at a hydrogen-producing temperature.
15. A method for starting operation of a hydrogen-producing fuel processing system, the method comprising:
electrically heating, during a startup period, a steam reforming region containing a steam reforming catalyst to a selected hydrogen-producing operating temperature of at least 200° C.; wherein when heated to the selected hydrogen-producing operating temperature, the steam reforming catalyst is configured to catalyze, via a steam reforming reaction, the formation of a mixed gas stream containing hydrogen gas as a majority component and other gases from a feed stream containing methanol and water that is delivered thereto;
ceasing the electrically heating;
delivering the feed stream to the steam reforming region;
producing the mixed gas stream from the feed stream;
separating the mixed gas stream into a hydrogen-rich stream, which contains hydrogen gas of greater purity than the mixed gas stream, and a byproduct stream, which contains at least a substantial portion of the other gases, utilizing at least one hydrogen-selective membrane, wherein the hydrogen-rich stream is formed from a portion of the mixed gas stream that passes through the at least one hydrogen-selective membrane and the byproduct stream is formed from a portion of the mixed gas stream that does not pass through the at least one hydrogen-selective membrane;
purifying the hydrogen-rich stream in a polishing region configured to reduce a concentration of at least one of the other gasses in the hydrogen-rich stream and produce a product hydrogen stream;
combusting at least a portion of the byproduct stream to produce a heated exhaust stream; and
heating the steam reforming region with the heated exhaust stream.
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This application is a continuation of and claims priority to U.S. patent application Ser. No. 12/189,378, which was filed on Aug. 11, 2008, issued on Oct. 26, 2010 as U.S. Pat. No. 7,819,955, and which is a continuation of U.S. patent application Ser. No. 11/726,387, which was filed on Mar. 20, 2007, issued on Aug. 12, 2008 as U.S. Pat. No. 7,410,531, and which is a continuation of U.S. patent application Ser. No. 11/441,931, which was filed on May 25, 2006, issued on Mar. 27, 2007 as U.S. Pat. No. 7,195,663, and which is a continuation of U.S. patent application Ser. No. 10/989,907, which was filed on Nov. 15, 2004, issued on May 30, 2006 as U.S. Pat. No. 7,052,530, and which is a continuation of U.S. patent application Ser. No. 10/728,473, which was filed on Dec. 5, 2003, issued on Nov. 30, 2004 as U.S. Pat. No. 6,824,593, and which is a continuation of U.S. patent application Ser. No. 10/430,110, which was filed on May 5, 2003, issued on Apr. 20, 2004 as U.S. Pat. No. 6,723,156, and which is a continuation of U.S. patent application Ser. No. 10/371,597, which was filed on Feb. 20, 2003, issued on Oct. 14, 2003 as U.S. Pat. No. 6,632,270, and which is a continuation of U.S. patent application Ser. No. 10/027,509, which was filed on Dec. 19, 2001, issued on Mar. 25, 2003 as U.S. Pat. No. 6,537,352. U.S. patent application Ser. No. 10/027,509 is a continuation-in-part of and claims priority to U.S. patent application Ser. Nos. 09/839,997, 09/618,866, and 09/967,172. U.S. patent application Ser. No. 09/839,997, was filed on Apr. 20, 2001, issued on Aug. 31, 2004 as U.S. Pat. No. 6,783,741, and is a continuation of U.S. patent application Ser. No. 09/291,447, which was filed on Apr. 13, 1999, issued on Apr. 24, 2001 U.S. Pat. No. 6,221,117, and which is a continuation-in-part application of U.S. patent application Ser. No. 08/951,091, which was filed on Oct. 15, 1997, issued on Dec. 7, 1999 as U.S. Pat. No. 5,997,594, and which is a continuation-in-part application of U.S. patent application Ser. No. 08/741,057, which was filed on Oct. 30, 1996, issued on Jan. 19, 1999 as U.S. Pat. No. 5,861,137. U.S. patent application Ser. No. 09/618,866, which was filed on Jul. 19, 2000, issued Apr. 15, 2003 as U.S. Pat. No. 6,547,858, and is a continuation-in-part application of U.S. patent application Ser. No. 09/274,154, which was filed on Mar. 22, 1999, issued on Nov. 28, 2000 as U.S. Pat. No. 6,152,995. U.S. patent application Ser. No. 09/618,866 also claims priority to U.S. Provisional Patent Application Ser. No. 60/191,891, which was filed on Mar. 23, 2000. U.S. patent application Ser. No. 09/967,172, which was filed on Sep. 27, 2001, issued on Dec. 17, 2002 as U.S. Pat. No. 6,494,937. The complete disclosures of the above-identified patent applications are hereby incorporated by reference for all purposes.
The present invention is related generally to the purification of hydrogen gas, and more specifically to hydrogen purification membranes, devices, and fuel processing and fuel cell systems containing the same.
Purified hydrogen is used in the manufacture of many products including metals, edible fats and oils, and semiconductors and microelectronics. Purified hydrogen is also an important fuel source for many energy conversion devices. For example, fuel cells use purified hydrogen and an oxidant to produce an electrical potential. Various processes and devices may be used to produce the hydrogen gas that is consumed by the fuel cells. However, many hydrogen-production processes produce an impure hydrogen stream, which may also be referred to as a mixed gas stream that contains hydrogen gas. Prior to delivering this stream to a fuel cell, a stack of fuel cells, or another hydrogen-consuming device, the mixed gas stream may be purified, such as to remove undesirable impurities.
A hydrogen purification device is schematically illustrated in
In the illustrated embodiment, the portion of the mixed gas stream that passes through the separation assembly enters a permeate region 32 of the internal compartment. This portion of the mixed gas stream forms hydrogen-rich stream 34, and the portion of the mixed gas stream that does not pass through the separation assembly forms a byproduct stream 36, which contains at least a substantial portion of the other gases. In some embodiments, byproduct stream 36 may contain a portion of the hydrogen gas present in the mixed gas stream. It is also within the scope of the disclosure that the separation assembly is adapted to trap or otherwise retain at least a substantial portion of the other gases, which will be removed as a byproduct stream as the assembly is replaced, regenerated or otherwise recharged. In
Device 10 is typically operated at elevated temperatures and/or pressures. For example, device 10 may be operated at (selected) temperatures in the range of ambient temperatures up to 700° C. or more. In many embodiments, the selected temperature will be in the range of 200° C. and 500° C., in other embodiments, the selected temperature will be in the range of 250° C. and 400° C. and in still other embodiments, the selected temperature will be 400° C.±either 25° C., 50° C. or 75° C. Device 10 may be operated at (selected) pressure in the range of approximately 50 psi and 1000 psi or more. In many embodiments, the selected pressure will be in the range of 50 psi and 250 or 500 psi, in other embodiments, the selected pressure will be less than 300 psi or less than 250 psi, and in still other embodiments, the selected pressure will be 175 psi±either 25 psi, 50 psi or 75 psi. As a result, the enclosure must be sufficiently well sealed to achieve and withstand the operating pressure.
It should be understood that as used herein with reference to operating parameters like temperature or pressure, the term “selected” refers to defined or predetermined threshold values or ranges of values, with device 10 and any associated components being configured to operate at or within these selected values. For further illustration, a selected operating temperature may be an operating temperature above or below a specific temperature, within a specific range of temperatures, or within a defined tolerance from a specific temperature, such as within 5%, 10%, etc. of a specific temperature.
In embodiments of the hydrogen purification device in which the device is operated at an elevated operating temperature, heat needs to be applied to, or generated within, the device to raise the temperature of the device to the selected operating temperature. For example, this heat may be provided by any suitable heating assembly 42. Illustrative examples of heating assembly 42 have been schematically illustrated in
A suitable structure for separation assembly 20 is one or more hydrogen-permeable and/or hydrogen-selective membranes 46, such as somewhat schematically illustrated in
Membrane 46 may be formed of any hydrogen-permeable material suitable for use in the operating environment and parameters in which purification device 10 is operated. Examples of suitable materials for membranes 46 include palladium and palladium alloys, and especially thin films of such metals and metal alloys. Palladium alloys have proven particularly effective, especially palladium with 35 wt % to 45 wt % copper. More specific examples of a palladium alloy that have proven effective include palladium-copper alloys containing 40 wt % (+/−0.25 or 0.5 wt %) copper, although other alloys and percentages are within the scope of the disclosure. Membranes 46 are typically formed from a thin foil that is approximately 0.001 inches thick. Accordingly, it should be understood that the thicknesses of the membranes illustrated herein have been exaggerated for purposes of illustration. It is within the scope of the present disclosure, however, that the membranes may be formed from hydrogen-permeable and/or hydrogen-selective materials, including metals and metal alloys other than those discussed above as well as non-metallic materials and compositions.
Metal membranes according to the present disclosure, and especially palladium and palladium alloy membranes, typically will also include relatively small amounts of at least one of carbon, silicon and oxygen, typically ranging from a few parts per million (ppm) to several hundred or more parts per million. For example, carbon may be introduced to the membrane either intentionally or unintentionally, such as from the raw materials from which the membranes are formed and/or through the handling and formation process. Because many lubricants are carbon-based, the machinery used in the formation and processing of the membranes may introduce carbon to the material from which the membranes are formed. Similarly, carbon-containing oils may be transferred to the material by direct or indirect contact with a user's body. Preferably, membranes constructed according to the present disclosure include less than 250 ppm carbon, and more preferably less than 150, 100 or 50 ppm carbon. Nonetheless, the membranes will typically still contain some carbon content, such as at least 5 or 10 ppm carbon. Therefore, it is within the scope of the disclosure that the membranes will contain carbon concentrations within the above ranges, such as approximately 5-150 or 10-150 ppm, 5-100 or 10-100 ppm, or 5-50 or 10-50 ppm carbon.
It is further within the scope of the disclosure that the membranes may include trace amounts of silicon and/or oxygen. For example, oxygen may be present in the Pd40Cu (or other alloy or metal) material in concentrations within the range of 5-200 ppm, including ranges of 5-100, 10-100, 5-50 and 10-50 ppm. Additionally or alternatively, silicon may be present in the material in concentrations in the range of 5-100 ppm, including ranges of 5-10 and 10-50 ppm.
In experiments, reducing the concentration of carbon in the membranes results in an increase in hydrogen flux, compared to a similar membrane that is used in similar operating conditions but which contains a greater concentration of carbon. Similarly, it is expected that increasing the oxygen and/or silicon concentrations will detrimentally affect the mechanical properties of the membrane. The following table demonstrates the correlation between high hydrogen permeability (represented as hydrogen flux through a 25 micron thick membrane at 100 psig hydrogen, 400 degrees Celsius) and low carbon content.
It is within the scope of the disclosure that the membranes may have a variety of thicknesses, including thicknesses that are greater or less than discussed above. For example, the membrane may be made thinner, with commensurate increase in hydrogen flux. Examples of suitable mechanisms for reducing the thickness of the membranes include rolling, sputtering and etching. A suitable etching process is disclosed in U.S. Pat. No. 6,152,995, the complete disclosure of which is hereby incorporated by reference for all purposes. Examples of various membranes, membrane configurations, and methods for preparing the same are disclosed in U.S. Pat. Nos. 6,221,117 and 6,319,306, the complete disclosures of which are hereby incorporated by reference for all purposes. The above-described “trace” components (carbon, oxygen and/or silicon) may be described as being secondary components of the material from which the membranes are formed, with palladium or a palladium alloy being referred to as the primary component. In practice, it is within the scope of the disclosure that these trace components may be alloyed with the palladium or palladium alloy material from which the membranes are formed or otherwise distributed or present within the membranes.
As discussed, membrane 46 may be formed of a hydrogen-permeable metal or metal alloy, such as palladium or a palladium alloy, including a palladium alloy that is essentially comprised of 60 wt % palladium and 40 wt % copper. Because palladium and palladium alloys are expensive, the thickness of the membrane should be minimal; i.e., as thin as possible without introducing an excessive number of holes in the membrane if it is desirable to reduce the expense of the membranes. Holes in the membrane are not desired because holes allow all gaseous components, including impurities, to pass through the membrane, thereby counteracting the hydrogen-selectivity of the membrane.
An example of a method for reducing the thickness of a hydrogen-permeable membrane is to roll form the membrane to be very thin, such as with thicknesses of less than approximately 50 microns, and more commonly with thicknesses of approximately 25 microns. The flux through a hydrogen-permeable metal membrane is inversely proportional to the membrane thickness. Therefore, by decreasing the thickness of the membrane, it is expected that the flux through the membrane will increase, and vice versa. In Table 2, below, the expected flux of hydrogen through various thicknesses of Pd-40Cu membranes is shown.
Besides the increase in flux obtained by decreasing the thickness of the membrane, the cost to obtain the membrane also increases as the membrane's thickness is reduced. Also, as the thickness of a membrane decreases, the membrane becomes more fragile and difficult to handle without damaging.
Through the etching process, or method, of the present disclosure, discussed in more detail subsequently, the thickness of a portion of the membrane, such as central region 8, may be selectively reduced, while leaving the remaining portion of the membrane, such as edge region 6, at its original thickness. Therefore, greater flux is obtained in the thinner etched region, while leaving a thicker, more durable edge region that bounds the central region and thereby provides support to the membrane.
For example, an etched membrane 46 prepared according to an etching method of the present disclosure is shown in
However, an unexpected benefit of chemically etching the membrane, as disclosed herein, is that the hydrogen flux through the etched region exceeds that expected or measured through roll-formed membranes of equal thickness. As shown below in Table 3, the method of the present disclosure yields a hydrogen-permeable metal membrane with significantly greater flux than unetched membranes of similar thicknesses.
As the above table demonstrates, the invented method produces hydrogen-permeable metal membranes that permit increased hydrogen throughput compared to unetched membranes of similar thickness by increasing the roughness and surface area of the etched region of the membrane. Perhaps more importantly, this increase in throughput is achieved without sacrificing selectivity for hydrogen or the purity of the harvested hydrogen gas, which is passed through the membrane.
Increasing the surface roughness of the membrane is especially beneficial as the thickness of the membrane is reduced to less than 25 microns, especially less than 20 microns. As the membrane thickness is reduced, the surface reaction rates governing the transport of gaseous molecular hydrogen onto the surface of the metal membrane become more important to the overall permeation rate of hydrogen across the membrane. In extreme cases in which the membrane is quite thin (less than approximately 15 microns) the surface reaction rates are significant in governing the overall permeation rate of hydrogen across the membrane. Therefore, increasing the surface area increases the rate of hydrogen permeation. This contrasts with relatively thick membranes (greater than 25 microns) in which the surface reaction rates are less important and the overall permeation rate of hydrogen across the membrane is governed by the bulk diffusion of hydrogen through the membrane.
Thus the etching process results in an overall reduction in the thickness of the membrane and an increase in the surface roughness (and surface area) of the membrane. These improvements yield an increase in hydrogen flux and reduce the amount of material (e.g., palladium alloy) that is required, while still maintaining the membrane's selectivity for hydrogen.
In the invented etching process, an etchant is used to selectively reduce the thickness of the membrane. When the etchant removes, or etches, material from the surface of a membrane, the etchant also increases the surface roughness and surface area of the membrane in the etched region.
Examples of suitable etchants include oxidizing agents and acids. An example of a suitable oxidizing acid is nitric acid. Other suitable examples include combinations of nitric acid with other acids, such as aqua regia (a mixture of 25 vol % concentrated nitric acid and 75 vol % concentrated hydrochloric acid). Another specific example of an etchant well-suited to use in the present disclosure is a mixture comprising 67 wt % concentrated nitric acid and 33 wt % aqueous solution of poly(vinyl alcohol). A suitable method of preparing the aqueous solution of poly(vinyl alcohol) is to dissolve 4 wt % of poly(vinyl alcohol) (average molecular weight 124,000 to 186,000; 87% to 89% hydrolyzed; Aldrich Chemical Company, Milwaukee, Wis.) in de-ionized water. The disclosed examples of etchants are for illustrative purposes, and should not be construed to be limiting examples. For example, the relative percentage of acid may be increased or decreased to make the etchant respectively more or less reactive, as desired.
In a first method of the present disclosure, a selected etchant is applied to at least one of the surfaces of the membrane. Once applied, the etchant removes material from the surface of the membrane, thereby increasing its surface roughness and reducing the thickness of the membrane in the etched region. After a defined time period, the etchant is removed. The etching process disclosed herein typically is conducted under ambient conditions (temperature and pressure), although it should be understood that the process could be conducted at elevated or reduced temperatures and pressures as well.
The etching process is limited either by the time during which the membrane is exposed to the etchant, or by the reactive elements of the etchant. In the latter scenario, it should be understood that the etching reaction is self-limiting, in that the reaction will reach an equilibrium state in which the concentration of dissolved membrane in the etchant solution remains relatively constant. Regardless of the limiting factor in the process, it is important to apply a volume and concentration of etchant for a time period that will not result in the etchant creating substantial holes in, or completely dissolving, the membrane. Preferably, no holes are created in the membrane during the etching process.
When applying the etchant to a surface of membrane 46, such as to produce membrane 17, it is desirable to control the region of the surface over which the etchant extends. It is also desirable to maintain an even distribution of etchant over this application region. If the application region of the etchant is not controlled, then the etchant may remove material from other non-desired regions of the membrane, such as the edge region, or may damage materials joined to the membrane, such as an attached frame. If an even distribution of etchant is not maintained, areas of increased etchant may have too much material removed, resulting in holes in the membrane. Similarly, other areas may not have enough material removed, resulting in less than the desired reduction in thickness and increase in flux.
To control the distribution of etchant within the desired application region, an absorbent medium is placed on the membrane and defines an application region to be etched. For example, in
Besides being selected to absorb the particular etchant without adversely reacting to the etchant or metal membrane, it is preferable that medium 33 has a substantially uniform absorbency and diffusivity along its length. When medium 33 absorbs and distributes the etchant uniformly along its length, it distributes the etchant evenly across the application region, thereby removing substantially the same amount of material across the entire application region. The benefit of this is not only that some etchant will contact, and thereby remove material from the entire application region, but also that the etchant will be uniformly distributed across the application region. Therefore, medium 33 prevents too much etchant being localized in an area, which would result in too much material being removed. In a region where too much etchant is applied, the excess etchant is drawn away from that region to other areas of the medium where less etchant is applied. Similarly, in a region where too little etchant is applied, the medium draws etchant to that region to produce an even distribution across the medium, and thereby across the application region.
As a result, the reduction of thickness in membrane 46 will be relatively uniform across the application region, and perhaps, more importantly, will be reproducible regardless of the exact rate and position at which the etchant is applied. Therefore, with the same size and type of medium 33 and the same volume of etchant 37, the resulting reduction in thickness should be reproducible for membranes of the same composition. Of course, it should be understood that etching removes material from the surface of the membrane, thereby resulting in an uneven, rough surface with increased surface area over an unetched surface. Therefore, the exact surface topography will not be seen. However, the average thickness measured across a section of the membrane should be reproducible. For example, in
Because medium 33 essentially defines the bounds of application region 35, medium 33 should be sized prior to placing it upon the surface to be etched. After placing the medium in the desired position on one of the membrane's surfaces, such as surface 2 shown in
The applied volume of etchant should be no more than a saturation volume of etchant. An absorbent medium can only absorb up to a defined volume of a particular etchant per unit of medium 33 before reaching the saturation point of the medium. Therefore, it is important not to exceed this saturation point. Too much applied etchant will result in unabsorbed etchant pooling on or adjacent to the medium, such as on the upper surface of medium 33 or around the edges of the medium. When excess etchant contacts the surface, it is likely to result in holes in the membrane because more than the desired amount of material is removed. As discussed, if these holes are numerous or large enough, they will render the membrane unusable for hydrogen purification applications, with any holes lowering the purity of the hydrogen passing through the membrane.
Therefore, to prevent too much etchant from being applied, the volume of etchant applied may approach, but should not exceed, the saturation volume of the etchant.
An example of a suitable absorbent medium is a cellulosic material, such as absorbent paper products. A particular example of an absorbent medium that has proven effective are single-fold paper towels manufactured by the Kimberly Clark company. When a three inch by three inch area of such a towel is used, approximately 2.5 mL of etchant may be applied without exceeding the saturation volume of that area. The capillary action of the cellulosic towel both absorbs the applied etchant and distributes the etchant throughout the towel. Other paper and cellulosic materials may be used as well, as long as they meet the criteria defined herein. Absorbent, diffusive materials other than cellulosic materials may be used as well.
After applying the etchant to medium 33, the etchant is allowed to remove material from the application region for a determined time period. This period is best determined through experimentation and will vary depending on such factors as the composition, thickness and desired thickness of the membrane, the absorbent medium being used, the composition and concentration of etchant, and the temperature at which the etching process is conducted. After this time period has passed, the medium is removed from the membrane, and the application, or treatment area is rinsed with water to remove any remaining etchant. After rinsing, the method may be repeated to etch another surface of the membrane.
Instead of a single etching step on each surface of the membrane, a variation of the above method includes plural etching steps for each surface to be etched. In the first step, a more reactive, or vigorous etchant is used to remove a substantial portion of the material to be removed. In the second step, a less reactive etchant is used to provide a more controlled, even etch across the application region.
As an illustrative example, Pd-40Cu alloy foil was etched first with concentrated nitric acid for 20-30 seconds using the absorbent medium technique described above. After removing the medium and rinsing and drying the membrane, a second etch with a mixture of 20 vol % neat ethylene glycol and the balance concentrated nitric acid was performed for between 1 and 4 minutes. Subsequent etching steps were performed with the glycol mixture to continue to gradually reduce the thickness of the membrane in the application region. Results of etching Pd-40Cu foil using this method are given in the table below.
Other than confining the etching solution to a desired application region, another benefit of using an absorbent medium to control the placement and distribution of the etchant is that the quantity of etchant (or etching solution) that may be applied without oversaturating the medium is limited. Thus, the etching reaction may be self-limiting, depending on the choice of and composition of etchant. For instance, varying the etching time using 33.3 wt % PVA solution/66.7 wt % concentrated HNO3 yielded the results shown in the following table. These results indicate that the volume of etchant that is applied at one time may limit the depth of etching, so long as the etchant is not so reactive or applied in sufficient quantity to completely dissolve the application region.
In a further variation of the etching method, a suitable mask may be applied to the membrane to define the boundaries of the region to be etched. For example, in
If the chemical etching process is not properly controlled, tiny holes will appear in the membrane. For example, in
One method for detecting any such holes is to utilize a light source to identify holes in the membrane. By shining a light on one side of the membrane, holes are detected where light shines through the other side of the membrane. The detected holes may then be repaired by spot electroplating, such as by using a Hunter Micro-Metallizer Pen available from Hunter Products, Inc., Bridgewater, N.J. In
The repairing step of the invented etching process also may be performed using a photolithographic method. In this case a light-sensitive, electrically insulating mask is applied to one surface of the membrane, and then the membrane is irradiated with light of the appropriate wavelength(s) from the opposite side. Any tiny holes that might be present in the membrane will allow the light to pass through the membrane and be absorbed by the light-sensitive mask. Next, the mask is washed to remove irradiated regions of the mask and thereby reveal the bare metal of the membrane. Because only the irradiated regions of the mask are removed, the remaining mask serves as an electrical insulator over the surface of the membrane. Then, all of the spots where the mask has been removed are electroplated or electrolessplated at the same time.
Because the patch, or plug, represents only a minute percentage of the surface area of the membrane, the patch may be formed from a material that is not hydrogen-permeable without the flux through the membrane being noticeably affected. Of course, a hydrogen-permeable and selective patch is preferred. Suitable metals for electroplating to fill or close tiny holes in the palladium-alloy membranes include copper, silver, gold, nickel, palladium, chromium, rhodium, and platinum. Volatile metals such as zinc, mercury, lead, bismuth and cadmium should be avoided. Furthermore, it is preferable that metal applied by plating be relatively free of phosphorous, carbon, sulfur and nitrogen, since these heteroatoms could contaminate large areas of the membrane and are generally known to reduce the permeability of palladium alloys to hydrogen.
In use, membrane 46 provides a mechanism for removing hydrogen from mixtures of gases because it selectively allows hydrogen to permeate through the membrane. The flowrate, or flux, of hydrogen through membrane 46 typically is accelerated by providing a pressure differential between a mixed gaseous mixture on one side of the membrane, and the side of the membrane to which hydrogen migrates, with the mixture side of the membrane being at a higher pressure than the other side.
Because of their extremely thin construction, membranes 46 typically are supported by at least one of a support or frame. Frames, or frame members, may be used to support the membranes from the perimeter regions of the membranes. Supports, or support assemblies, typically support the membranes by extending across and in contact with at least a substantial portion of one or more of the membrane surfaces, such as surfaces 2 or 19. By referring briefly back to
Supports 54, frames 15 and mounts 52 should be thermally and chemically stable under the operating conditions of device 10, and support 54 should be sufficiently porous or contain sufficient voids to allow hydrogen that permeates membrane 46 to pass substantially unimpeded through the support layer. Examples of support layer materials include metal, carbon, and ceramic foam, porous and microporous ceramics, porous and microporous metals, metal mesh, perforated metal, and slotted metal. Additional examples include woven metal mesh (also known as screen) and tubular metal tension springs.
In embodiments of the disclosure in which membrane 46 is a metal membrane and the support and/or frame also are formed from metal, it is preferable that the support or frame is composed of metal that is formed from a corrosion-resistant material. Examples of such materials include corrosion-resistant alloys, such as stainless steels and non-ferrous corrosion-resistant alloys comprised of one or more of the following metals: chromium, nickel, titanium, niobium, vanadium, zirconium, tantalum, molybdenum, tungsten, silicon, and aluminum. These corrosion-resistant alloys have a native surface oxide layer that is chemically and physically very stable and serves to significantly retard the rate of intermetallic diffusion between the thin metal membrane and the metal support layer. Such intermetallic diffusion, if it were to occur, often results in degradation of the hydrogen permeability of the membrane and is undesirable.
Although membrane 46 is illustrated in
The tubular membranes may have a variety of configurations and constructions, such as those discussed above with respect to the planar membranes shown in
As discussed, enclosure 12 defines a pressurized compartment 18 in which separation assembly 20 is positioned. In the embodiments shown in
Another illustrative example of a suitable configuration for an end plate 60 is shown in
End plates 60 and perimeter shell 62 are secured together by a retention structure 72. Structure 72 may take any suitable form capable of maintaining the components of enclosure 12 together in a fluid-tight or substantially fluid-tight configuration in the operating parameters and conditions in which device 10 is used. Examples of suitable structures 72 include welds 74 and bolts 76, such as shown in
In the lower halves of
In FIGS. 9 and 11-12, the illustrated enclosures include a pair of end plates 60 and a shell 62. With reference to
As an alternative to a pair of end plates 60 joined by a separate perimeter shell 62, enclosure 12 may include a shell that is at least partially integrated with either or both of the end plates. For example, in
A benefit of shell 62 being integrally formed with at least one of the end plates is that the enclosure has one less interface that must be sealed. This benefit may be realized by reduced leaks due to the reduced number of seals that could fail, fewer components, and/or a reduced assembly time for device 10. Another example of such a construction for enclosure 12 is shown in
Before proceeding to additional illustrative configurations for end plates 60, it should be clarified that as used herein in connection with the enclosures of devices 10, the term “interface” is meant to refer to the interconnection and sealing region that extends between the portions of enclosure 12 that are separately formed and thereafter secured together, such as (but not necessarily) by one of the previously discussed retention structures 72. The specific geometry and size of interface 94 will tend to vary, such as depending upon size, configuration and nature of the components being joined together. Therefore, interface 94 may include a metal-on-metal seal formed between corresponding end regions and perimeter regions, a metal-on-metal seal formed between corresponding pairs of end regions, a metal-gasket (or other seal member 82)-metal seal, etc. Similarly, the interface may have a variety of shapes, including linear, arcuate and rectilinear configurations that are largely defined by the shape and relative position of the components being joined together.
For example, in
It should be understood that any of these interfaces may be used with an enclosure constructed according to the present disclosure. However, for purposes of brevity, every embodiment of enclosure 12 will not be shown with each of these interfaces. Although somewhat schematically illustrated in the previously discussed figures, it should be understood that embodiments of device 10 that include end plates 60 may include end plates having a variety of configurations, such as those disclosed in the patent applications incorporated herein. Therefore, although the subsequently described end plates shown in
Consider for example a circular end plate formed from Type 304 stainless steel and having a uniform thickness of 0.75 inches. Such an end plate weights 7.5 pounds. A hydrogen purification device containing this end plate was exposed to operating parameters of 400° C. and 175 psi. Maximum stresses of 25,900 psi were imparted to the end plate, with a maximum deflection of 0.0042 inches and a deflection at perimeter region 90 of 0.0025 inches.
Another end plate 60 constructed according to the present disclosure is shown in
Unlike the previously illustrated end plates, however, the central region of the end plate has a variable thickness between its interior and exterior surfaces, which is perhaps best seen in
A reduction in weight means that a purification device 10 that includes the end plate will be lighter than a corresponding purification device that includes a similarly constructed end plate formed without region 132. With the reduction in weight also comes a corresponding reduction in the amount of heat (thermal energy) that must be applied to the end plate to heat the end plate to a selected operating temperature. In the illustrated embodiment, region 132 also increases the surface area of exterior surface 124. Increasing the surface area of the end plate compared to a corresponding end plate may, but does not necessarily in all embodiments, increase the heat transfer surface of the end plate, which in turn, can reduce the heating requirements and/or time of a device containing end plate 120.
In some embodiments, plate 120 may also be described as having a cavity that corresponds to, or includes, the region of maximum stress on a similarly constructed end plate in which the cavity was not present. Accordingly, when exposed to the same operating parameters and conditions, lower stresses will be imparted to end plate 120 than to a solid end plate formed without region 132. For example, in the solid end plate with a uniform thickness, the region of maximum stress occurs within the portion of the end plate occupied by removed region 132 in end plate 120. Accordingly, an end plate with region 132 may additionally or alternatively be described as having a stress abatement structure 134 in that an area of maximum stress that would otherwise be imparted to the end plate has been removed.
For purposes of comparison, consider an end plate 120 having the configuration shown in
For purposes of comparison, consider an end plate 120 having the configuration shown in
As a further example, forming plate 120′ with a region 132 having a diameter of 3.75 inches instead of 3.25 inches decreases the weight of the end plate to 5.3 pounds and produced the same maximum deflection. This variation produces a maximum stress that is less than 25,000 psi, although approximately 5% greater than that of end plate 120′ (24,700 psi, compared to 23,500 psi). At perimeter region 90, this variation of end plate 120′ exhibited a maximum deflection of 0.0068 inches.
Also shown in dashed lines in FIGS. 19 and 21-22 are guide structures 144. Guide structures 144 extend into compartment 18 and provide supports that may be used to position and/or align separation assembly 20, such as membranes 46. In some embodiments, guide structures 144 may themselves form mounts 52 for the separation assembly. In other embodiments, the device includes mounts other than guide structures 144. Guide structures may be used with any of the end plates illustrated, incorporated and/or described herein, regardless of whether any such guide structures are shown in a particular drawing figure. However, it should also be understood that hydrogen purification devices according to the present disclosure may be formed without guide structures 144. In embodiments of device 10 that include guide structures 144 that extend into or through compartment 18, the number of such structures may vary from a single support to two or more supports. Similarly, while guide structures 144 have been illustrated as cylindrical ribs or projections, other shapes and configurations may be used within the scope of the disclosure.
Guide structures 144 may be formed from the same materials as the corresponding end plates. Additionally or alternatively, the guide structures may include a coating or layer of a different material. Guide structures 144 may be either separately formed from the end plates and subsequently attached thereto, or integrally formed therewith. Guide structures 144 may be coupled to the end plates by any suitable mechanism, including attaching the guide structures to the interior surfaces of the end plates, inserting the guide structures into bores extending partially through the end plates from the interior surfaces thereof, or inserting the guide structures through bores that extend completely through the end plates. In embodiments where the end plates include bores that extend completely through the end plates (which are graphically illustrated for purposes of illustration at 146 in
For purposes of comparison, end plate 150 has a reduced weight compared to end plates 120 and 120′. Plate 150 weighed 4.7 pounds and experienced maximum stresses of 25,000 psi or less when subjected to the operating parameters discussed above (400° C. and 175 psi). The maximum deflection of the plate was 0.0098 inches, and the displacement at perimeter region 90 was 0.0061 inches.
Another illustrative example of a suitable configuration for end plate 60 is shown in
Truss assembly 162 extends from exterior surface 124 of base plate 164 and includes a plurality of projecting ribs 166 that extend from exterior surface 124. In
End plate 160 may additionally, or alternatively, be described as having a support (170) that extends in a spaced-apart relationship beyond exterior surface 124 of base plate 164 and which is adapted to provide additional stiffness and/or strength to the base plate. Still another additional or alternative description of end plate 160 is that the end plate includes heat transfer structure (162) extending away from the exterior surface of the base plate, and that the heat transfer structure includes a surface (170) that is spaced-away from surface 124 such that a heated fluid stream may pass between the surfaces.
Truss assembly 162 may also be referred to as an example of a deflection abatement structure because it reduces the deflection that would otherwise occur if base plate 164 were formed without the truss assembly. Similarly, truss assembly 162 may also provide another example of a stress abatement restructure because it reduces the maximum stresses that would otherwise be imparted to the base plate. Furthermore, the open design of the truss assembly increases the heat transfer area of the base plate without adding significant weight to the base plate.
Continuing the preceding comparisons between end plates, plate 160 was subjected to the same operating parameters as the previously described end plates. The maximum stresses imparted to base plate 164 were 10,000 psi or less. Similarly, the maximum deflection of the base plate was only 0.0061 inches, with a deflection of 0.0056 inches at perimeter region 90. It should be noted, that base plate 160 achieved this significant reduction in maximum stress while weighing only 3.3 pounds. Similarly, base plate 164 experienced a smaller maximum displacement and comparable or reduced perimeter displacement yet had a base plate that was only 0.25 inches thick. Of course, plate 160 may be constructed with thicker base plates, but the tested plate proved to be sufficiently strong and rigid under the operating parameters with which it was used.
As discussed, enclosure 12 may include a pair of end plates 60 and a perimeter shell. In
It is also within the scope of the disclosure that enclosure 12 may include stress and/or deflection abatement structures that extend into compartment 18 as opposed to, or in addition to, corresponding structures that extend from the exterior surface of the end plates. In
As discussed, the dimensions of device 10 and enclosure 12 may also vary. For example, an enclosure designed to house tubular separation membranes may need to be longer (i.e. have a greater distance between end plates) than an enclosure designed to house planar separation membranes to provide a comparable amount of membrane surface area exposed to the mixed gas stream (i.e., the same amount of effective membrane surface area). Similarly, an enclosure configured to house planar separation membranes may tend to be wider (i.e., have a greater cross-sectional area measured generally parallel to the end plates) than an enclosure designed to house tubular separation membranes. However, it should be understood that neither of these relationships are required, and that the specific size of the device and/or enclosure may vary. Factors that may affect the specific size of the enclosure include the type and size of separation assembly to be housed, the operating parameters in which the device will be used, the flow rate of mixed gas stream 24, the shape and configuration of devices such as heating assemblies, fuel processors and the like with which or within which the device will be used, and to some degree, user preferences.
As discussed previously, hydrogen purification devices may be operated at elevated temperatures and/or pressures. Both of these operating parameters may impact the design of enclosures 12 and other components of the devices. For example, consider a hydrogen purification device 10 operated at a selected operating temperature above an ambient temperature, such as a device operating at 400° C. As an initial matter, the device, including enclosure 12 and separation assembly 20, must be constructed from a material that can withstand the selected operating temperature, and especially over prolonged periods of time and/or with repeated heating and cooling off cycles. Similarly, the materials that are exposed to the gas streams preferably are not reactive or at least not detrimentally reactive with the gases. An example of a suitable material is stainless steel, such as Type 304 stainless steel, although others may be used.
Besides the thermal and reactive stability described above, operating device 10 at a selected elevated temperature requires one or more heating assemblies 42 to heat the device to the selected operating temperature. When the device is initially operated from a shutdown, or unheated, state, there will be an initial startup or preheating period in which the device is heated to the selected operating temperature. During this period, the device may not produce a hydrogen-rich stream at all, a hydrogen-rich stream that contains more than an acceptable level of the other gases, and/or a reduced flow rate of the hydrogen-rich stream compared to the byproduct stream or streams (meaning that a greater percentage of the hydrogen gas is being exhausted as byproduct instead of product). In addition to the time to heat the device, one must also consider the heat or thermal energy required to heat the device to the selected temperature. The heating assembly or assemblies may add to the operating cost, materials cost, and/or equipment cost of the device. For example, a simplified end plate 60 is a relatively thick slab having a uniform thickness. In fact, stainless steel plates having a uniform thickness of 0.5 inches or 0.75 inches have proven effective to support and withstand the operating parameters and conditions of device 10. However, the dimensions of these plates add considerable weight to device 10, and in many embodiments require considerable thermal energy to be heated to the selected operating temperature. As used herein, the term “uniform thickness” is meant to refer to devices that have a constant or at least substantially constant thickness, including those that deviate in thickness by a few percent (less than 5%) along their lengths. In contrast, and as used herein, a “variable thickness” will refer to a thickness that varies by at least 10%, and in some embodiments at least 25%, 40% or 50%.
The pressure at which device 10 is operated may also affect the design of device 10, including enclosure 12 and separation assembly 20. Consider for example a device operating at a selected pressure of 175 psi. Device 10 must be constructed to be able to withstand the stresses encountered when operating at the selected pressure. This strength requirement affects not only the seals formed between the components of enclosure 12, but also the stresses imparted to the components themselves. For example, deflection or other deformation of the end plates and/or shell may cause gases within compartment 18 to leak from the enclosure. Similarly, deflection and/or deformation of the components of the device may also cause unintentional mixing of two or more of gas streams 24, 34 and 36. For example, an end plate may deform plastically or elastically when subjected to the operating parameters under which device 10 is used. Plastic deformation results in a permanent deformation of the end plate, the disadvantage of which appears fairly evident. Elastic deformation, however, also may impair the operation of the device because the deformation may result in internal and/or external leaks. More specifically, the deformation of the end plates or other components of enclosure 12 may enable gases to pass through regions where fluid-tight seals previously existed. As discussed, device 10 may include gaskets or other seal members to reduce the tendency of these seals to leak, however, the gaskets have a finite size within which they can effectively prevent or limit leaks between opposing surfaces. For example, internal leaks may occur in embodiments that include one or more membrane envelopes or membrane plates compressed (with or without gaskets) between the end plates. As the end plates deform and deflect away from each other, the plates and/or gaskets may in those regions not be under the same tension or compression as existed prior to the deformation. Gaskets, or gasket plates, may be located between a membrane envelope and adjacent feed plates, end plates, and/or other adjacent membrane envelopes. Similarly, gaskets or gasket plates may also be positioned within a membrane envelope to provide additional leak prevention within the envelope.
In view of the above, it can be seen that there are several competing factors to be weighed with respect to device 10. In the context of enclosure 12, the heating requirements of the enclosure will tend to increase as the materials used to form the enclosure are thickened. To some degree using thicker materials may increase the strength of the enclosure, however, it may also increase the heating and material requirements, and in some embodiments actually produce regions to which greater stresses are imparted compared to a thinner enclosure. Areas to monitor on an end plate include the deflection of the end plate, especially at the perimeter regions that form interface(s) 94, and the stresses imparted to the end plate.
As discussed, enclosure 12 contains an internal compartment 18 that houses separation assembly 20, such as one or more separation membranes 46, which are supported within the enclosure by a suitable mount 52. In the illustrative examples shown in
An example of a membrane envelope is shown in
As discussed, a support 54 may be used to support the membranes against high feed pressures. Support 54 should enable gas that permeates through membranes 46 to flow therethrough. Support 54 includes surfaces 211 against which the permeate surfaces 50 of the membranes are supported. In the context of a pair of membranes forming a membrane envelope, support 54 may also be described as defining harvesting conduit 204. In conduit 204, permeated gas preferably may flow both transverse and parallel to the surface of the membrane through which the gas passes, such as schematically illustrated in
An example of a suitable support 54 for membrane envelopes 200 is shown in
The screen members may be of similar or the same construction, and more or less screen members may be used than shown in
During fabrication of the membrane envelopes, adhesive may be used to secure membranes 46 to the screen structure and/or to secure the components of screen structure 210 together, as discussed in more detail in the above-incorporated U.S. patent application Ser. No. 09/812,499. For purposes of illustration, adhesive is generally indicated in dashed lines at 218 in
Supports 54, including screen structure 210, may include a coating 219 on the surfaces 211 that engage membranes 46, such as indicated in dash-dot lines in
The hydrogen purification devices 10 described, illustrated and/or incorporated herein may include one or more membrane envelopes 200, typically along with suitable input and output ports through which the mixed gas stream is delivered and from which the hydrogen-rich and byproduct streams are removed. In some embodiments, the device may include a plurality of membrane envelopes. When the separation assembly includes a plurality of membrane envelopes, it may include fluid conduits interconnecting the envelopes, such as to deliver a mixed gas stream thereto, to withdraw the hydrogen-rich stream therefrom, and/or to withdraw the gas that does not pass through the membranes from mixed gas region 30. When the device includes a plurality of membrane envelopes, the permeate stream, byproduct stream, or both, from a first membrane envelope may be sent to another membrane envelope for further purification. The envelope or plurality of envelopes and associated ports, supports, conduits and the like may be referred to as a membrane module 220.
The number of membrane envelopes 200 used in a particular device 10 depends to a degree upon the feed rate of mixed gas stream 24. For example, a membrane module 220 containing four envelopes 200 has proven effective for a mixed gas stream delivered to device 10 at a flow rate of 20 liters/minute. As the flow rate is increased, the number of membrane envelopes may be increased, such as in a generally linear relationship. For example, a device 10 adapted to receive mixed gas stream 24 at a flow rate of 30 liters/minute may preferably include six membrane envelopes. However, these exemplary numbers of envelopes are provided for purposes of illustration, and greater or fewer numbers of envelopes may be used. For example, factors that may affect the number of envelopes to be used include the hydrogen flux through the membranes, the effective surface area of the membranes, the flow rate of mixed gas stream 24, the desired purity of hydrogen-rich stream 34, the desired efficiency at which hydrogen gas is removed from mixed gas stream 24, user preferences, the available dimensions of device 10 and compartment 18, etc.
Preferably, but not necessarily, the screen structure and membranes that are incorporated into a membrane envelope 200 include frame members 230, or plates, that are adapted to seal, support and/or interconnect the membrane envelopes. An illustrative example of suitable frame members 230 is shown in
Continuing the above illustration of exemplary frame members 230, permeate gaskets 236 and 236′ are attached to permeate frame 232, preferably but not necessarily, by using another thin application of adhesive. Next, membranes 46 are supported against screen structure 210 and/or attached to screen structure 210 using a thin application of adhesive, such as by spraying or otherwise applying the adhesive to either or both of the membrane and/or screen structure. Care should be taken to ensure that the membranes are flat and firmly attached to the corresponding screen member 212. Feed plates, or gaskets, 238 and 238′ are optionally attached to gaskets 236 and 236′, such as by using another thin application of adhesive. The resulting membrane envelope 200 is then positioned within compartment 18, such as by a suitable mount 52. Optionally, two or more membrane envelopes may be stacked or otherwise supported together within compartment 18.
As a further alternative, each membrane 46 may be fixed to a frame member 230, such as a metal frame 240, as shown in
For purposes of illustration, a suitable geometry of fluid flow through membrane envelope 200 is described with respect to the embodiment of envelope 200 shown in
As discussed, device 10 may include a single membrane 46 within shell 62, a plurality of membranes within shell 62, one or more membrane envelopes 200 within shell 62 and/or other separation assemblies 20. In
Shell 62 has been described as interconnecting the end plates to define therewith internal compartment 18. It is within the scope of the disclosure that the shell may be formed from a plurality of interconnected plates 230. For example, a membrane module 220 that includes one or more membrane envelopes 200 may form shell 62 because the perimeter regions of each of the plates may form a fluid-tight, or at least substantially fluid-tight seal therebetween. An example of such a construction is shown in
In the preceding discussion, illustrative examples of suitable materials of construction and methods of fabrication for the components of hydrogen purification devices according to the present disclosure have been discussed. It should be understood that the examples are not meant to represent an exclusive, or closed, list of exemplary materials and methods, and that it is within the scope of the disclosure that other materials and/or methods may be used. For example, in many of the above examples, desirable characteristics or properties are presented to provide guidance for selecting additional methods and/or materials. This guidance is also meant as an illustrative aid, as opposed to reciting essential requirements for all embodiments.
As discussed, in embodiments of device 10 that include a separation assembly that includes hydrogen-permeable and/or hydrogen-selective membranes 46, suitable materials for membranes 46 include palladium and palladium alloys, including alloys containing relatively small amounts of carbon, silicon and/or oxygen. As also discussed, the membranes may be supported by frames and/or supports, such as the previously described frames 240, supports 54 and screen structure 210. Furthermore, devices 10 are often operated at selected operating parameters that include elevated temperatures and pressures. In such an application, the devices typically begin at a startup, or initial, operating state, in which the devices are typically at ambient temperature and pressure, such as atmospheric pressure and a temperature of approximately 25° C. From this state, the device is heated (such as with heating assembly 42) and pressurized (via any suitable mechanism) to selected operating parameters, such as temperatures of 200° C. or more, and selected operating pressures, such as pressure of 50 psi or more.
When devices 10 are heated, the components of the devices will expand. The degree to which the components enlarge or expand is largely defined by the coefficient of thermal expansion (CTE) of the materials from which the components are formed. Accordingly, these differences in CTEs will tend to cause the components to expand at different rates, thereby placing additional tension or compression on some components and/or reduced tension or compression on others.
For example, consider a hydrogen-selective membrane 46 formed from an alloy of 60 wt % palladium and 40 wt % copper (Pd-40Cu). Such a membrane has a coefficient of thermal expansion of 13.4 (μm/m)/° C. Further consider that the membrane is secured to a structural frame 230 or retained against a support 54 formed from a material having a different CTE than Pd-40Cu or another material from which membrane 46 is formed. When a device 10 in which these components are operated is heated from an ambient or resting configuration, the components will expand at different rates. If the CTE of the membrane is less than the CTE of the adjoining structural component, then the membrane will tend to be stretched as the components are heated. In addition to this initial stretching, it should be considered that hydrogen purification devices typically experience thermal cycling as they are heated for use, then cooled or allowed to cool when not in use, then reheated, recooled, etc. In such an application, the stretched membrane may become wrinkled as it is compressed toward its original configuration as the membrane and other structural component(s) are cooled. On the other hand, if the CTE of the membrane is greater than the CTE of the adjoining structural component, then the membrane will tend to be compressed during heating of the device, and this compression may cause wrinkling of the membrane. During cooling, or as the components cool, the membrane is then drawn back to its original configuration.
Wrinkling of membrane 46 may cause holes and cracks in the membrane, especially along the wrinkles where the membrane is fatigued. In regions where two or more wrinkles intersect, the likelihood of holes and/or cracks is increased because that portion of the membrane has been wrinkled in at least two different directions. It should be understood that holes and cracks lessen the selectivity of the membrane for hydrogen gas because the holes and/or cracks are not selective for hydrogen gas and instead allow any of the components of the mixed gas stream to pass thereto. During repeated thermal cycling of the membrane, these points or regions of failure will tend to increase in size, thereby further decreasing the purity of the hydrogen-rich, or permeate, stream.
One approach to guarding against membrane failure due to differences in CTE between the membranes and adjoining structural components is to place deformable gaskets between the membrane and any component of device 10 that contacts the membrane and has sufficient stiffness or structure to impart compressive or tensile forces to the membrane that may wrinkle the membrane. For example, in
In embodiments where either or both of these frames are not formed from a deformable material (i.e., a resilient material that may be compressed or expanded as forces are imparted thereto and which returns to its original configuration upon removal of those forces), when membrane 46 is mounted on a plate 242 that has a thickness and/or composition that may exert the above-described wrinkling tensile or compressive forces to membrane 46, or when support 54 is bonded (or secured under the selected operating pressure) to membrane 46, a different approach may additionally or alternatively be used. More specifically, the life of the membranes may be increased by forming components of device 10 that otherwise would impart wrinkling forces, either tensile or compressive, to membrane 46 from materials having a CTE that is the same or similar to that of the material or materials from which membrane 46 is formed.
For example, Type 304 stainless steel has a CTE of 17.3 and Type 316 stainless steel has a CTE of 16.0. Accordingly, Type 304 stainless steel has a CTE that is approximately 30% greater than that of Pd-40Cu, and Type 316 stainless steel has a CTE that is approximately 20% greater than that of Pd-40Cu. This does not mean that these materials may not be used to form the various supports, frames, plates, shells and the like discussed herein. However, in some embodiments of the disclosure, it may be desirable to form at least some of these components form a material that has a CTE that is the same or similar to that of the material from which membrane 46 is formed. More specifically, it may be desirable to have a CTE that is the same as the CTE of the material from which membrane 46 is formed, or a material that has a CTE that is within a selected range of the CTE of the material from which membrane 46 is selected, such as within ±1%, 2%, 5%, 10%, or 15%.
In the following table, exemplary alloys and their corresponding CTE's and compositions are presented.
From the above information, it can be seen that alloys such as Hastelloy X have a CTE that corresponds to that of Pd-40Cu, and that the Monel and Inconel 601 alloys have CTE's that are within approximately 1% of the CTE of Pd-40Cu. Of the illustrative example of materials listed in the table, all of the alloys other than Hastelloy F, Incoloy 800 and the Type 300 series of stainless steel alloys have CTE's that are within 2% of the CTE of Pd-40Cu, and all of the alloys except Type 304, 316 and 310S stainless steel alloys have CTE's that are within 5% of the CTE of Pd-40Cu.
Examples of components of device 10 that may be formed from a material having a selected CTE relative to membrane 46, such as a CTE corresponding to or within one of the selected ranges of the CTE of membrane 46, include one or more of the following: support 54, screen members 212, fine or outer screen or expanded metal member 216, inner screen member 214, membrane frame 240, permeate frame 232, permeate plate 234, feed plate 238. By the above, it should be understood that one of the above components may be formed from such a material, more than one of the above components may be formed from such a material, but that none of the above components are required to be formed from such a material. Similarly, the membranes 46 may be formed from materials other than Pd-40Cu, and as such the selected CTE's will vary depending upon the particular composition of membranes 46.
By way of further illustration, a device 10 may be formed with a membrane module 220 that includes one or more membrane envelopes 200 with a screen structure that is entirely formed from a material having one of the selected CTE's; only outer, or membrane-contacting, screen members (such as members 216) formed from a material having one of the selected CTE's and the inner member or members being formed from a material that does not have one of the selected CTE's; inner screen member 214 formed from a material having one of the selected CTE's, with the membrane-contacting members being formed from a material that does not have one of the selected CTE's, etc. By way of further illustration, a device 10 may have a single membrane 46 supported between the end plates 60 of the enclosure by one or more mounts 52 and/or one or more supports 54. The mounts and/or the supports may be formed from a material having one of the selected CTE's. Similarly, at least a portion of enclosure 12, such as one or both of end plates 60 or shell 62, may be formed from a material having one of the selected CTE's.
In embodiments of device 10 in which there are components of the device that do not directly contact membrane 46, these components may still be formed from a material having one of the selected CTE's. For example, a portion or all of enclosure 12, such as one or both of end plates 60 or shell 62, may be formed from a material, including one of the alloys listed in Table 6, having one of the selected CTE's relative to the CTE of the material from which membrane 46 is formed even though these portions do not directly contact membrane 46.
A hydrogen purification device 10 constructed according to the present disclosure may be coupled to, or in fluid communication with, any source of impure hydrogen gas. Examples of these sources include gas storage devices, such as hydride beds and pressurized tanks. Another source is an apparatus that produces as a byproduct, exhaust or waste stream a flow of gas from which hydrogen gas may be recovered. Still another source is a fuel processor, which as used herein, refers to any device that is adapted to produce a mixed gas stream containing hydrogen gas from at least one feed stream containing a feedstock. Typically, hydrogen gas will form a majority or at least a substantial portion of the mixed gas stream produced by a fuel processor.
A fuel processor may produce mixed gas stream 24 through a variety of mechanisms. Examples of suitable mechanisms include steam reforming and autothermal reforming, in which reforming catalysts are used to produce hydrogen gas from a feed stream containing a carbon-containing feedstock and water. Other suitable mechanisms for producing hydrogen gas include pyrolysis and catalytic partial oxidation of a carbon-containing feedstock, in which case the feed stream does not contain water. Still another suitable mechanism for producing hydrogen gas is electrolysis, in which case the feedstock is water. Examples of suitable carbon-containing feedstocks include at least one hydrocarbon or alcohol. Examples of suitable hydrocarbons include methane, propane, natural gas, diesel, kerosene, gasoline and the like. Examples of suitable alcohols include methanol, ethanol, and polyols, such as ethylene glycol and propylene glycol.
A hydrogen purification device 10 adapted to receive mixed gas stream 24 from a fuel processor is shown schematically in
Fuel processors are often operated at elevated temperatures and/or pressures. As a result, it may be desirable to at least partially integrate hydrogen purification device 10 with fuel processor 300, as opposed to having device 10 and fuel processor 300 connected by external fluid transportation conduits. An example of such a configuration is shown in
As discussed, fuel processor 300 is any suitable device that produces a mixed gas stream containing hydrogen gas, and preferably a mixed gas stream that contains a majority of hydrogen gas. For purposes of illustration, the following discussion will describe fuel processor 300 as being adapted to receive a feed stream 316 containing a carbon-containing feedstock 318 and water 320, as shown in
Feed stream 316 may be delivered to fuel processor 300 via any suitable mechanism. A single feed stream 316 is shown in
As generally indicated at 332 in
Fuel processor 300 may, but does not necessarily, further include a polishing region 348, such as shown in dashed lines in
Region 348 includes any suitable structure for removing or reducing the concentration of the selected compositions in stream 34. For example, when the product stream is intended for use in a PEM fuel cell stack or other device that will be damaged if the stream contains more than determined concentrations of carbon monoxide or carbon dioxide, it may be desirable to include at least one methanation catalyst bed 350. Bed 350 converts carbon monoxide and carbon dioxide into methane and water, both of which will not damage a PEM fuel cell stack. Polishing region 348 may also include another hydrogen-producing region 352, such as another reforming catalyst bed, to convert any unreacted feedstock into hydrogen gas. In such an embodiment, it is preferable that the second reforming catalyst bed is upstream from the methanation catalyst bed so as not to reintroduce carbon dioxide or carbon monoxide downstream of the methanation catalyst bed.
Steam reformers typically operate at temperatures in the range of 200° C. and 700° C., and at pressures in the range of 50 psi and 1000 psi, although temperatures outside of this range are within the scope of the disclosure, such as depending upon the particular type and configuration of fuel processor being used. Any suitable heating mechanism or device may be used to provide this heat, such as a heater, burner, combustion catalyst, or the like. The heating assembly may be external the fuel processor or may form a combustion chamber that forms part of the fuel processor. The fuel for the heating assembly may be provided by the fuel processing or fuel cell system, by an external source, or both.
It is further within the scope of the disclosure that one or more of the components of fuel processor 300 may either extend beyond the shell or be located external at least shell 312. For example, device 10 may extend at least partially beyond shell 312, as indicated in
As indicated above, fuel processor 300 may be adapted to deliver hydrogen-rich stream 34 or product hydrogen stream 314 to at least one fuel cell stack, which produces an electric current therefrom. In such a configuration, the fuel processor and fuel cell stack may be referred to as a fuel cell system. An example of such a system is schematically illustrated in
Fuel cell stack 322 contains at least one, and typically multiple, fuel cells 324 that are adapted to produce an electric current from the portion of the product hydrogen stream 314 delivered thereto. This electric current may be used to satisfy the energy demands, or applied load, of an associated energy-consuming device 325. Illustrative examples of devices 325 include, but should not be limited to, a motor vehicle, recreational vehicle, boat, tools, lights or lighting assemblies, appliances (such as household or other appliances), household, signaling or communication equipment, etc. It should be understood that device 325 is schematically illustrated in
The above-identified and incorporated patents and patent applications contain numerous examples of fuel processors according to the present disclosure. For purposes of illustration, representative examples of steam reformers with separation regions that include one or more membranes 46 according to the present disclosure are shown. In view of the preceding incorporations by reference, each component, subcomponent, and variation will not be represented and discussed below and/or indicated with reference numbers in the subsequently described figures. Similarly, where possible, like reference numbers will be used. It should be understood that the following discussion is intended to provide exemplary constructions for steam reformers according to the present disclosure, and that any of the above-described features, elements, subelements and/or variations may be incorporated into any of these reformers.
Within reforming region 332 a reforming catalyst 334 (e.g., BASF catalyst K3-110 or ICI catalyst 52-8) reacts with the vaporized feed stream to produce mixed gas stream 24 in the vicinity of a separation region that contains a hydrogen-selective membrane 46. As discussed, membrane 46 may have any of the compositions and constructions described and incorporated herein, including the relatively low carbon content construction described above. As shown, membrane 46 includes end caps 436 and is supported by a support 54 in the form of a tension spring 58.
As discussed previously, hydrogen-rich stream 34 is formed from the portion of mixed gas stream 24 that passes through membrane 46, with the remaining portion of the mixed gas stream forming byproduct stream 36. Hydrogen-rich stream 34 travels within permeate region 32, which as illustrated within tubular membrane 46 may be described as a transport region to a polishing region 348, which in the illustrated embodiment is contained at least partially within region 32. As shown, region 348 contains both a reforming catalyst bed, or region, 352 downstream of membrane 46, as well as a methanation catalyst bed, or region, 350 downstream from the reforming catalyst bed. As discussed, the catalyst beds or regions may form part of a single catalyst bed or may be spaced-apart from each other. Similarly, the beds may vary in relative size and number. Also shown for purposes of illustration in
As discussed, byproduct stream 36 may contain hydrogen and other gases that may be used or stored for other applications, including as a combustion fuel to provide some or all of the heating requirements of reformer 400. In the illustrated embodiment, reformer 400 is configured so that stream 36 flows into combustion region 460 and is ignited by a combustion catalyst 462.
Reformer 400″ includes an outer shell 312 sealed at each end by end plates 453. As shown, bolts are used to secure the end plates to the shoulders, or flanges, of a tubular portion of shell 312. However, it is within the scope of the disclosure that other fastening mechanisms may be used and that at least one of the end plates may be integrally formed with the rest of the shell. To illustrate that a variety of internal configurations are possible for reformers according to the present disclosure, reformer 400″ includes a reforming region 332 through which a tubular combustion region 460 extends, in contrast to the tubular reforming region within a combustion region shown in
Reformer 400″ also demonstrates that one or more of the reformers fluid conduits may extend external shell 312. For example, reformer 400″ includes a conduit 470 through which byproduct stream 36 flows. In the illustrated embodiment, conduit 470 includes a valve assembly 473, which may include a pressure let-down valve and/or other types of flow-regulating valves to deliver stream 36 at the desired pressure for utilization as a combustion fuel within the pressurized reformer. As shown, conduit 470 delivers stream 36 to an intake manifold 477. Manifold 477 includes an air inlet 434, e.g., coupled to an air blower or to discharged air from the cathode component of a fuel cell stack or to another suitable air source, and air passage way 471 in which the air and fuel stream are mixed and which is in communication with combustion region 460, which as shown has a coiled configuration. In
Reformer 500 also demonstrates an example of a steam reformer (or fuel processor) utilizing an attached hydrogen-purification device 10 in the form of a separation assembly 20 containing a plurality of at least generally planar hydrogen-selective membranes 46 and/or membrane envelopes. As discussed, membranes 46 may have a variety of compositions and constructions, including the relatively low carbon-content membranes (such as Pd-40Cu or other palladium or palladium alloy membranes) discussed above. As shown, conduit 470 delivers byproduct stream 36 to intake manifold 477.
Reformer 500′ also provides an illustrative example of a reformer in which at least a portion of the reforming region extends beyond shell 312. As shown in
In the illustrated embodiment, tubes 530 are heated by hot combustion gases passing from internal combustion manifold 534 to internal exhaust manifold 536, and ultimately exiting reformer 500′ through outlet 438. In
Coil 430 a should be of sufficient length that the feedstock is vaporized prior to reaching distribution manifold 528. It should be understood that the circuitous path of coil 430 a is shown in
From distribution manifold 528, the vaporized feedstock is distributed to steam reforming tubes 530 and the mixed gas streams 24 generated therein are delivered to a separation assembly, which in the illustrated embodiment takes the form of a membrane module having a plurality of membrane envelopes 200 that each contain hydrogen-selective membranes 46.
Reformer 500″ includes the previously described conduit 470, which as discussed may be configured to deliver at least a portion of stream 36 to combustion region 460. Also shown in
To illustrate another example of a portion of the reformer being located external shell 312, reformer 500′ is shown with a polishing region 348 located external shell 312. As shown, region 348 extends proximate the exterior surface 540 of shell 312. However, it is within the scope of the disclosure that region 348 may be at least partially or completely positioned against or spaced away from shell 312. Polishing region 348 is further heated by the hydrogen-rich stream 24 that flows into the bed from the separation region 20. Finally, purified hydrogen exits reformer 500′ as stream 314. By locating the polishing catalyst bed external shell 312, reformer 500′ may either include additional reforming tubes within its shell, or the shell may be smaller because it no longer needs to house the polishing catalyst bed.
The reformer shown in
To increase the energy efficiency and to increase the combustion chamber temperature within the reformer, reformer 500″ includes a quenching chamber 562 adapted to partially quench the reformate gas stream prior to its entrance into separation region 20, which as discussed may contain one or more membranes 46 and/or membrane envelopes 200. As shown, the reformate gas stream must pass through chamber 562 after exiting reforming tubes 530 and prior to entering region 20. Chamber 562 includes a pair of ports 564 and 566 through which combustion air respectively enters and exits the chamber. The air is cooler than the reformate gas stream, and therefore cools the reformate gas stream prior to its entry into the separation region. During this exchange, the combustion air is heated prior to its entry to burner 503.
The quenching chamber and external vaporization coils described with respect to reformer 500″ may be used with any of the reformers (or fuel processors) described, illustrated and/or incorporated herein. Similarly, the external polishing catalyst bed may be used with any of the reformers described herein, such as to increase the number of reforming tubes within the reformer's shells or to decrease the size of the shell.
The invented hydrogen purification membranes, devices and fuel processing systems are applicable to the fuel processing, fuel cell and other industries in which hydrogen gas is produced and/or utilized.
It is believed that the disclosure set forth above encompasses multiple distinct inventions with independent utility. While each of these inventions has been disclosed in its preferred form, the specific embodiments thereof as disclosed and illustrated herein are not to be considered in a limiting sense as numerous variations are possible. The subject matter of the inventions includes all novel and non-obvious combinations and subcombinations of the various elements, features, functions and/or properties disclosed herein. Similarly, where the claims recite “a” or “a first” element or the equivalent thereof, such claims should be understood to include incorporation of one or more such elements, neither requiring nor excluding two or more such elements.
It is believed that the following claims particularly point out certain combinations and subcombinations that are directed to one of the disclosed inventions and are novel and non-obvious. Inventions embodied in other combinations and subcombinations of features, functions, elements and/or properties may be claimed through amendment of the present claims or presentation of new claims in this or a related application. Such amended or new claims, whether they are directed to a different invention or directed to the same invention, whether different, broader, narrower or equal in scope to the original claims, are also regarded as included within the subject matter of the inventions of the present disclosure.
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